Wireless communication devices may be able to communicate with other wireless communication devices using device-to-device (D2D) communication in a broad sense. In D2D communication (which may be interchangeably referred to as proximity service (ProSe) or peer-to-peer communication), the source and the target are wireless devices. Thus, using D2D communication, a first wireless device, such as a first user equipment (UE), may be able to receive signals from and/or transmit signals directly to another UE, and vice versa. D2D communication may allow off-loading of the cellular network, faster communication, increased awareness of surrounding wireless devices of interest (e.g., running the same application), higher-quality links due to a shorter distance, etc. D2D communication is being considered for a variety of applications, including video streaming, online gaming, media downloading, peer-to-peer (P2P), file sharing, etc. In 3GPP, ProSe currently comprises at least ProSe Direct Communication and ProSe Direct Discovery, as described in 3GPP TS 23.303 V13.0.0 (2015-06).
FIG. 1 is a schematic block diagram of an example D2D system architecture 100. More particularly, FIG. 1 illustrates an example D2D system architecture 100 in a Long Term Evolution (LTE) network. D2D system architecture 100 includes Evolved UMTS Terrestrial Radio Access Network (E-UTRAN) 105, one or more UEs 110, ProSe APP 115, Evolved Packet Core (EPC) 120, ProSe Function 125, and ProSe APP Server 130. E-UTRAN 105 is a radio access network that may include a combination of UEs 110, such as UEs 110A and 110B, and one or more network nodes, such as one or more eNodeBs.
UEs 110A and 110B may be any type of wireless device communicating with a node and/or with another wireless device in a cellular or mobile communication system. UEs 110A and 110B communicate with E-UTRAN 105 over an LTE-Uu radio interface. UEs 110A and 110B include ProSe APP 115A and ProSe APP 115B, respectively. ProSe APP 115A and 115B may be application layer components that allow UEs 110A and 110B to perform D2D operations. EPC 120 of D2D system architecture 100 is the core network of the LTE system. EPC 120 may include any suitable configuration of hardware and/or software. For example, EPC 120 may include a home subscriber server, a serving gateway, a packet data network gateway, or any other suitable components. E-UTRAN 105 may communicate with EPC 120 over an S1 interface.
ProSe Function 125 and ProSe App Server 130 facilitate D2D communication between UE 110A and UE 110B. ProSe Function 125 is a logical function that may be used for network related actions required for D2D communications. The role of ProSe Function 125 may vary according to particular ProSe features. In some cases, there may be one logical ProSe Function 125 in each public land mobile network (PLMN) that supports Proximity Services. ProSe Function 125 may determine the resources used for D2D communication links (e.g., every second uplink subframe, one subframe per radio frame, etc.).
In Long Term Evolution (LTE), the Power Headroom Reporting (PHR) procedure is used to provide the serving network node (e.g., eNodeB (eNB)) with information about a difference between the nominal UE maximum transmit power and the estimated power for uplink shared channel (UL-SCH) transmission per activated Serving Cell. PHR procedure also provides the serving network node with information about the difference between the nominal UE maximum power and the estimated power for UL-SCH and physical uplink control channel (PUCCH) transmission on the Primary Cell (PCell).
In LTE, the PHR range is from −23 to +40 dB. If the Power Headroom value is (+), it indicates that the wireless device still has some space under the maximum power. If the Power Headroom value is (−), it indicates that the calculated uplink (UL) transmit power is above the UE maximum.